Rollup merge of #94146 - est31:let_else, r=cjgillot

Adopt let else in more places

Continuation of #89933, #91018, #91481, #93046, #93590, #94011.

I have extended my clippy lint to also recognize tuple passing and match statements. The diff caused by fixing it is way above 1 thousand lines. Thus, I split it up into multiple pull requests to make reviewing easier. This is the biggest of these PRs and handles the changes outside of rustdoc, rustc_typeck, rustc_const_eval, rustc_trait_selection, which were handled in PRs #94139, #94142, #94143, #94144.

compiler/rustc_ast_lowering/src/asm.rs

@@ -339,9 +339,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
                                     let idx2 = *o.get();
                                     let &(ref op2, op_sp2) = &operands[idx2];
-                                    let reg2 = match op2.reg() {
-                                        Some(asm::InlineAsmRegOrRegClass::Reg(r)) => r,
-                                        _ => unreachable!(),
+                                    let Some(asm::InlineAsmRegOrRegClass::Reg(reg2)) = op2.reg() else {
+                                        unreachable!();
                                     };
 
                                     let msg = format!(

compiler/rustc_ast_lowering/src/expr.rs

@@ -330,9 +330,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
         args: Vec<AstP<Expr>>,
         legacy_args_idx: &[usize],
     ) -> hir::ExprKind<'hir> {
-        let path = match f.kind {
-            ExprKind::Path(None, ref mut path) => path,
-            _ => unreachable!(),
+        let ExprKind::Path(None, ref mut path) = f.kind else {
+            unreachable!();
         };
 
         // Split the arguments into const generics and normal arguments

compiler/rustc_ast_lowering/src/item.rs

@@ -1376,9 +1376,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
         // keep track of the Span info. Now, `add_implicitly_sized` in `AstConv` checks both param bounds and
         // where clauses for `?Sized`.
         for pred in &generics.where_clause.predicates {
-            let bound_pred = match *pred {
-                WherePredicate::BoundPredicate(ref bound_pred) => bound_pred,
-                _ => continue,
+            let WherePredicate::BoundPredicate(ref bound_pred) = *pred else {
+                continue;
             };
             let compute_is_param = || {
                 // Check if the where clause type is a plain type parameter.

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -482,9 +482,8 @@ impl<'a> AstValidator<'a> {
     }
 
     fn check_foreign_kind_bodyless(&self, ident: Ident, kind: &str, body: Option<Span>) {
-        let body = match body {
-            None => return,
-            Some(body) => body,
+        let Some(body) = body else {
+            return;
         };
         self.err_handler()
             .struct_span_err(ident.span, &format!("incorrect `{}` inside `extern` block", kind))
@@ -504,9 +503,8 @@ impl<'a> AstValidator<'a> {
 
     /// An `fn` in `extern { ... }` cannot have a body `{ ... }`.
     fn check_foreign_fn_bodyless(&self, ident: Ident, body: Option<&Block>) {
-        let body = match body {
-            None => return,
-            Some(body) => body,
+        let Some(body) = body else {
+            return;
         };
         self.err_handler()
             .struct_span_err(ident.span, "incorrect function inside `extern` block")

compiler/rustc_ast_passes/src/show_span.rs

@@ -57,9 +57,8 @@ impl<'a> Visitor<'a> for ShowSpanVisitor<'a> {
 }
 
 pub fn run(span_diagnostic: &rustc_errors::Handler, mode: &str, krate: &ast::Crate) {
-    let mode = match mode.parse().ok() {
-        Some(mode) => mode,
-        None => return,
+    let Ok(mode) = mode.parse() else {
+        return;
     };
     let mut v = ShowSpanVisitor { span_diagnostic, mode };
     visit::walk_crate(&mut v, krate);

compiler/rustc_attr/src/builtin.rs

@@ -556,17 +556,14 @@ pub fn eval_condition(
                     return false;
                 }
             };
-            let min_version = match parse_version(min_version.as_str(), false) {
-                Some(ver) => ver,
-                None => {
-                    sess.span_diagnostic
-                        .struct_span_warn(
-                            *span,
-                            "unknown version literal format, assuming it refers to a future version",
-                        )
-                        .emit();
-                    return false;
-                }
+            let Some(min_version) = parse_version(min_version.as_str(), false) else {
+                sess.span_diagnostic
+                    .struct_span_warn(
+                        *span,
+                        "unknown version literal format, assuming it refers to a future version",
+                    )
+                    .emit();
+                return false;
             };
             let rustc_version = parse_version(env!("CFG_RELEASE"), true).unwrap();
 
@@ -669,9 +666,8 @@ where
             break;
         }
 
-        let meta = match attr.meta() {
-            Some(meta) => meta,
-            None => continue,
+        let Some(meta) = attr.meta() else {
+            continue;
         };
         let mut since = None;
         let mut note = None;

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -2071,22 +2071,17 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                         ) = rvalue
                         {
                             for operand in operands {
-                                let assigned_from = match operand {
-                                    Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
-                                        assigned_from
-                                    }
-                                    _ => continue,
+                                let (Operand::Copy(assigned_from) | Operand::Move(assigned_from)) = operand else {
+                                    continue;
                                 };
                                 debug!(
                                     "annotate_argument_and_return_for_borrow: assigned_from={:?}",
                                     assigned_from
                                 );
 
                                 // Find the local from the operand.
-                                let assigned_from_local = match assigned_from.local_or_deref_local()
-                                {
-                                    Some(local) => local,
-                                    None => continue,
+                                let Some(assigned_from_local) = assigned_from.local_or_deref_local() else {
+                                    continue;
                                 };
 
                                 if assigned_from_local != target {
@@ -2138,10 +2133,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                         );
 
                         // Find the local from the rvalue.
-                        let assigned_from_local = match assigned_from.local_or_deref_local() {
-                            Some(local) => local,
-                            None => continue,
-                        };
+                        let Some(assigned_from_local) = assigned_from.local_or_deref_local() else { continue };
                         debug!(
                             "annotate_argument_and_return_for_borrow: \
                              assigned_from_local={:?}",
@@ -2189,11 +2181,8 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                         assigned_to, args
                     );
                     for operand in args {
-                        let assigned_from = match operand {
-                            Operand::Copy(assigned_from) | Operand::Move(assigned_from) => {
-                                assigned_from
-                            }
-                            _ => continue,
+                        let (Operand::Copy(assigned_from) | Operand::Move(assigned_from)) = operand else {
+                            continue;
                         };
                         debug!(
                             "annotate_argument_and_return_for_borrow: assigned_from={:?}",

compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs

@@ -650,13 +650,10 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 
                 // The only kind of statement that we care about is assignments...
                 if let StatementKind::Assign(box (place, rvalue)) = &stmt.kind {
-                    let into = match place.local_or_deref_local() {
-                        Some(into) => into,
-                        None => {
-                            // Continue at the next location.
-                            queue.push(current_location.successor_within_block());
-                            continue;
-                        }
+                    let Some(into) = place.local_or_deref_local() else {
+                        // Continue at the next location.
+                        queue.push(current_location.successor_within_block());
+                        continue;
                     };
 
                     match rvalue {

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -444,10 +444,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     debug!("borrowed_content_source: init={:?}", init);
                     // We're only interested in statements that initialized a value, not the
                     // initializations from arguments.
-                    let loc = match init.location {
-                        InitLocation::Statement(stmt) => stmt,
-                        _ => continue,
-                    };
+                    let InitLocation::Statement(loc) = init.location else { continue };
 
                     let bbd = &self.body[loc.block];
                     let is_terminator = bbd.statements.len() == loc.statement_index;
@@ -787,9 +784,8 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
     ) -> UseSpans<'tcx> {
         use self::UseSpans::*;
 
-        let stmt = match self.body[location.block].statements.get(location.statement_index) {
-            Some(stmt) => stmt,
-            None => return OtherUse(self.body.source_info(location).span),
+        let Some(stmt) = self.body[location.block].statements.get(location.statement_index) else {
+            return OtherUse(self.body.source_info(location).span);
         };
 
         debug!("move_spans: moved_place={:?} location={:?} stmt={:?}", moved_place, location, stmt);

compiler/rustc_borrowck/src/diagnostics/move_errors.rs

@@ -188,10 +188,9 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
             }
             // Error with the pattern
             LookupResult::Exact(_) => {
-                let mpi = match self.move_data.rev_lookup.find(move_from.as_ref()) {
-                    LookupResult::Parent(Some(mpi)) => mpi,
+                let LookupResult::Parent(Some(mpi)) = self.move_data.rev_lookup.find(move_from.as_ref()) else {
                     // move_from should be a projection from match_place.
-                    _ => unreachable!("Probably not unreachable..."),
+                    unreachable!("Probably not unreachable...");
                 };
                 for ge in &mut *grouped_errors {
                     if let GroupedMoveError::MovesFromValue {

compiler/rustc_borrowck/src/lib.rs

@@ -1914,10 +1914,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             // without going over a Deref.
             let mut shortest_uninit_seen = None;
             for prefix in this.prefixes(base, PrefixSet::Shallow) {
-                let mpi = match this.move_path_for_place(prefix) {
-                    Some(mpi) => mpi,
-                    None => continue,
-                };
+                let Some(mpi) = this.move_path_for_place(prefix) else { continue };
 
                 if maybe_uninits.contains(mpi) {
                     debug!(

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -913,9 +913,8 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         let TypeTest { generic_kind, lower_bound, locations, verify_bound: _ } = type_test;
 
         let generic_ty = generic_kind.to_ty(tcx);
-        let subject = match self.try_promote_type_test_subject(infcx, generic_ty) {
-            Some(s) => s,
-            None => return false,
+        let Some(subject) = self.try_promote_type_test_subject(infcx, generic_ty) else {
+            return false;
         };
 
         // For each region outlived by lower_bound find a non-local,
@@ -1623,15 +1622,14 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         // If we have some bound universal region `'a`, then the only
         // elements it can contain is itself -- we don't know anything
         // else about it!
-        let error_element = match {
+        let Some(error_element) = ({
             self.scc_values.elements_contained_in(longer_fr_scc).find(|element| match element {
                 RegionElement::Location(_) => true,
                 RegionElement::RootUniversalRegion(_) => true,
                 RegionElement::PlaceholderRegion(placeholder1) => placeholder != *placeholder1,
             })
-        } {
-            Some(v) => v,
-            None => return,
+        }) else {
+            return;
         };
         debug!("check_bound_universal_region: error_element = {:?}", error_element);
 

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -810,13 +810,12 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
                 ty::Adt(adt_def, substs) => (&adt_def.variants[variant_index], substs),
                 ty::Generator(def_id, substs, _) => {
                     let mut variants = substs.as_generator().state_tys(def_id, tcx);
-                    let mut variant = match variants.nth(variant_index.into()) {
-                        Some(v) => v,
-                        None => bug!(
+                    let Some(mut variant) = variants.nth(variant_index.into()) else {
+                        bug!(
                             "variant_index of generator out of range: {:?}/{:?}",
                             variant_index,
                             substs.as_generator().state_tys(def_id, tcx).count()
-                        ),
+                        );
                     };
                     return match variant.nth(field.index()) {
                         Some(ty) => Ok(ty),
@@ -2178,35 +2177,29 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                     }
 
                     CastKind::Pointer(PointerCast::MutToConstPointer) => {
-                        let ty_from = match op.ty(body, tcx).kind() {
-                            ty::RawPtr(ty::TypeAndMut {
-                                ty: ty_from,
-                                mutbl: hir::Mutability::Mut,
-                            }) => ty_from,
-                            _ => {
-                                span_mirbug!(
-                                    self,
-                                    rvalue,
-                                    "unexpected base type for cast {:?}",
-                                    ty,
-                                );
-                                return;
-                            }
+                        let ty::RawPtr(ty::TypeAndMut {
+                            ty: ty_from,
+                            mutbl: hir::Mutability::Mut,
+                        }) = op.ty(body, tcx).kind() else {
+                            span_mirbug!(
+                                self,
+                                rvalue,
+                                "unexpected base type for cast {:?}",
+                                ty,
+                            );
+                            return;
                         };
-                        let ty_to = match ty.kind() {
-                            ty::RawPtr(ty::TypeAndMut {
-                                ty: ty_to,
-                                mutbl: hir::Mutability::Not,
-                            }) => ty_to,
-                            _ => {
-                                span_mirbug!(
-                                    self,
-                                    rvalue,
-                                    "unexpected target type for cast {:?}",
-                                    ty,
-                                );
-                                return;
-                            }
+                        let ty::RawPtr(ty::TypeAndMut {
+                            ty: ty_to,
+                            mutbl: hir::Mutability::Not,
+                        }) = ty.kind() else {
+                            span_mirbug!(
+                                self,
+                                rvalue,
+                                "unexpected target type for cast {:?}",
+                                ty,
+                            );
+                            return;
                         };
                         if let Err(terr) = self.sub_types(
                             *ty_from,
@@ -2238,17 +2231,14 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                             _ => None,
                         };
 
-                        let (ty_elem, ty_mut) = match opt_ty_elem_mut {
-                            Some(ty_elem_mut) => ty_elem_mut,
-                            None => {
-                                span_mirbug!(
-                                    self,
-                                    rvalue,
-                                    "ArrayToPointer cast from unexpected type {:?}",
-                                    ty_from,
-                                );
-                                return;
-                            }
+                        let Some((ty_elem, ty_mut)) = opt_ty_elem_mut else {
+                            span_mirbug!(
+                                self,
+                                rvalue,
+                                "ArrayToPointer cast from unexpected type {:?}",
+                                ty_from,
+                            );
+                            return;
                         };
 
                         let (ty_to, ty_to_mut) = match ty.kind() {

compiler/rustc_borrowck/src/universal_regions.rs

@@ -641,9 +641,8 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
                 let (&output, tuplized_inputs) =
                     inputs_and_output.skip_binder().split_last().unwrap();
                 assert_eq!(tuplized_inputs.len(), 1, "multiple closure inputs");
-                let inputs = match tuplized_inputs[0].kind() {
-                    ty::Tuple(inputs) => inputs,
-                    _ => bug!("closure inputs not a tuple: {:?}", tuplized_inputs[0]),
+                let ty::Tuple(inputs) = tuplized_inputs[0].kind() else {
+                    bug!("closure inputs not a tuple: {:?}", tuplized_inputs[0]);
                 };
 
                 ty::Binder::bind_with_vars(

compiler/rustc_builtin_macros/src/cfg_accessible.rs

@@ -44,9 +44,8 @@ impl MultiItemModifier for Expander {
             template,
         );
 
-        let path = match validate_input(ecx, meta_item) {
-            Some(path) => path,
-            None => return ExpandResult::Ready(Vec::new()),
+        let Some(path) = validate_input(ecx, meta_item) else {
+            return ExpandResult::Ready(Vec::new());
         };
 
         match ecx.resolver.cfg_accessible(ecx.current_expansion.id, path) {

compiler/rustc_builtin_macros/src/compile_error.rs

@@ -9,9 +9,8 @@ pub fn expand_compile_error<'cx>(
     sp: Span,
     tts: TokenStream,
 ) -> Box<dyn base::MacResult + 'cx> {
-    let var = match get_single_str_from_tts(cx, sp, tts, "compile_error!") {
-        None => return DummyResult::any(sp),
-        Some(v) => v,
+    let Some(var) = get_single_str_from_tts(cx, sp, tts, "compile_error!") else {
+        return DummyResult::any(sp);
     };
 
     cx.span_err(sp, &var);